ArgumentPromotion.cpp revision e3a8830c1d263b41ee114d7cb3fd50d240ec32b3
1//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass promotes "by reference" arguments to be "by value" arguments. In 11// practice, this means looking for internal functions that have pointer 12// arguments. If it can prove, through the use of alias analysis, that an 13// argument is *only* loaded, then it can pass the value into the function 14// instead of the address of the value. This can cause recursive simplification 15// of code and lead to the elimination of allocas (especially in C++ template 16// code like the STL). 17// 18// This pass also handles aggregate arguments that are passed into a function, 19// scalarizing them if the elements of the aggregate are only loaded. Note that 20// it refuses to scalarize aggregates which would require passing in more than 21// three operands to the function, because passing thousands of operands for a 22// large array or structure is unprofitable! 23// 24// Note that this transformation could also be done for arguments that are only 25// stored to (returning the value instead), but does not currently. This case 26// would be best handled when and if LLVM begins supporting multiple return 27// values from functions. 28// 29//===----------------------------------------------------------------------===// 30 31#define DEBUG_TYPE "argpromotion" 32#include "llvm/Transforms/IPO.h" 33#include "llvm/Constants.h" 34#include "llvm/DerivedTypes.h" 35#include "llvm/Module.h" 36#include "llvm/CallGraphSCCPass.h" 37#include "llvm/Instructions.h" 38#include "llvm/ParameterAttributes.h" 39#include "llvm/Analysis/AliasAnalysis.h" 40#include "llvm/Analysis/CallGraph.h" 41#include "llvm/Target/TargetData.h" 42#include "llvm/Support/CallSite.h" 43#include "llvm/Support/CFG.h" 44#include "llvm/Support/Debug.h" 45#include "llvm/ADT/DepthFirstIterator.h" 46#include "llvm/ADT/Statistic.h" 47#include "llvm/ADT/StringExtras.h" 48#include "llvm/Support/Compiler.h" 49#include <set> 50using namespace llvm; 51 52STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 53STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 54STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 55STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 56 57namespace { 58 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass. 59 /// 60 struct VISIBILITY_HIDDEN ArgPromotion : public CallGraphSCCPass { 61 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 62 AU.addRequired<AliasAnalysis>(); 63 AU.addRequired<TargetData>(); 64 CallGraphSCCPass::getAnalysisUsage(AU); 65 } 66 67 virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC); 68 static char ID; // Pass identification, replacement for typeid 69 ArgPromotion() : CallGraphSCCPass((intptr_t)&ID) {} 70 71 private: 72 bool PromoteArguments(CallGraphNode *CGN); 73 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const; 74 Function *DoPromotion(Function *F, 75 SmallPtrSet<Argument*, 8> &ArgsToPromote, 76 SmallPtrSet<Argument*, 8> &ByValArgsToTransform); 77 }; 78 79 char ArgPromotion::ID = 0; 80 RegisterPass<ArgPromotion> X("argpromotion", 81 "Promote 'by reference' arguments to scalars"); 82} 83 84Pass *llvm::createArgumentPromotionPass() { 85 return new ArgPromotion(); 86} 87 88bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) { 89 bool Changed = false, LocalChange; 90 91 do { // Iterate until we stop promoting from this SCC. 92 LocalChange = false; 93 // Attempt to promote arguments from all functions in this SCC. 94 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 95 LocalChange |= PromoteArguments(SCC[i]); 96 Changed |= LocalChange; // Remember that we changed something. 97 } while (LocalChange); 98 99 return Changed; 100} 101 102/// PromoteArguments - This method checks the specified function to see if there 103/// are any promotable arguments and if it is safe to promote the function (for 104/// example, all callers are direct). If safe to promote some arguments, it 105/// calls the DoPromotion method. 106/// 107bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 108 Function *F = CGN->getFunction(); 109 110 // Make sure that it is local to this module. 111 if (!F || !F->hasInternalLinkage()) return false; 112 113 // First check: see if there are any pointer arguments! If not, quick exit. 114 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 115 unsigned ArgNo = 0; 116 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 117 I != E; ++I, ++ArgNo) 118 if (isa<PointerType>(I->getType())) 119 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 120 if (PointerArgs.empty()) return false; 121 122 // Second check: make sure that all callers are direct callers. We can't 123 // transform functions that have indirect callers. 124 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); 125 UI != E; ++UI) { 126 CallSite CS = CallSite::get(*UI); 127 if (!CS.getInstruction()) // "Taking the address" of the function 128 return false; 129 130 // Ensure that this call site is CALLING the function, not passing it as 131 // an argument. 132 if (UI.getOperandNo() != 0) 133 return false; 134 } 135 136 // Check to see which arguments are promotable. If an argument is promotable, 137 // add it to ArgsToPromote. 138 SmallPtrSet<Argument*, 8> ArgsToPromote; 139 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 140 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 141 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, ParamAttr::ByVal); 142 143 // If this is a byval argument, and if the aggregate type is small, just 144 // pass the elements, which is always safe. 145 Argument *PtrArg = PointerArgs[i].first; 146 if (isByVal) { 147 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 148 if (const StructType *STy = dyn_cast<StructType>(AgTy)) 149 if (STy->getNumElements() <= 3) { 150 // If all the elements are first class types, we can promote it. 151 bool AllSimple = true; 152 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 153 if (!STy->getElementType(i)->isFirstClassType()) { 154 AllSimple = false; 155 break; 156 } 157 158 // Safe to transform, don't even bother trying to "promote" it. 159 // Passing the elements as a scalar will allow scalarrepl to hack on 160 // the new alloca we introduce. 161 if (AllSimple) { 162 ByValArgsToTransform.insert(PtrArg); 163 continue; 164 } 165 } 166 } 167 168 // Otherwise, see if we can promote the pointer to its value. 169 if (isSafeToPromoteArgument(PtrArg, isByVal)) 170 ArgsToPromote.insert(PtrArg); 171 } 172 173 // No promotable pointer arguments. 174 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) return false; 175 176 Function *NewF = DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 177 178 // Update the call graph to know that the function has been transformed. 179 getAnalysis<CallGraph>().changeFunction(F, NewF); 180 return true; 181} 182 183/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 184/// to load. 185static bool IsAlwaysValidPointer(Value *V) { 186 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 187 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 188 return IsAlwaysValidPointer(GEP->getOperand(0)); 189 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 190 if (CE->getOpcode() == Instruction::GetElementPtr) 191 return IsAlwaysValidPointer(CE->getOperand(0)); 192 193 return false; 194} 195 196/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 197/// all callees pass in a valid pointer for the specified function argument. 198static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 199 Function *Callee = Arg->getParent(); 200 201 unsigned ArgNo = std::distance(Callee->arg_begin(), 202 Function::arg_iterator(Arg)); 203 204 // Look at all call sites of the function. At this pointer we know we only 205 // have direct callees. 206 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 207 UI != E; ++UI) { 208 CallSite CS = CallSite::get(*UI); 209 assert(CS.getInstruction() && "Should only have direct calls!"); 210 211 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 212 return false; 213 } 214 return true; 215} 216 217 218/// isSafeToPromoteArgument - As you might guess from the name of this method, 219/// it checks to see if it is both safe and useful to promote the argument. 220/// This method limits promotion of aggregates to only promote up to three 221/// elements of the aggregate in order to avoid exploding the number of 222/// arguments passed in. 223bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 224 // We can only promote this argument if all of the uses are loads, or are GEP 225 // instructions (with constant indices) that are subsequently loaded. 226 227 // We can also only promote the load if we can guarantee that it will happen. 228 // Promoting a load causes the load to be unconditionally executed in the 229 // caller, so we can't turn a conditional load into an unconditional load in 230 // general. 231 bool SafeToUnconditionallyLoad = false; 232 if (isByVal) // ByVal arguments are always safe to load from. 233 SafeToUnconditionallyLoad = true; 234 235 BasicBlock *EntryBlock = Arg->getParent()->begin(); 236 SmallVector<LoadInst*, 16> Loads; 237 std::vector<SmallVector<ConstantInt*, 8> > GEPIndices; 238 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 239 UI != E; ++UI) 240 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 241 if (LI->isVolatile()) return false; // Don't hack volatile loads 242 Loads.push_back(LI); 243 244 // If this load occurs in the entry block, then the pointer is 245 // unconditionally loaded. 246 SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock; 247 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 248 if (GEP->use_empty()) { 249 // Dead GEP's cause trouble later. Just remove them if we run into 250 // them. 251 getAnalysis<AliasAnalysis>().deleteValue(GEP); 252 GEP->eraseFromParent(); 253 return isSafeToPromoteArgument(Arg, isByVal); 254 } 255 // Ensure that all of the indices are constants. 256 SmallVector<ConstantInt*, 8> Operands; 257 for (unsigned i = 1, e = GEP->getNumOperands(); i != e; ++i) 258 if (ConstantInt *C = dyn_cast<ConstantInt>(GEP->getOperand(i))) 259 Operands.push_back(C); 260 else 261 return false; // Not a constant operand GEP! 262 263 // Ensure that the only users of the GEP are load instructions. 264 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 265 UI != E; ++UI) 266 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 267 if (LI->isVolatile()) return false; // Don't hack volatile loads 268 Loads.push_back(LI); 269 270 // If this load occurs in the entry block, then the pointer is 271 // unconditionally loaded. 272 SafeToUnconditionallyLoad |= LI->getParent() == EntryBlock; 273 } else { 274 return false; 275 } 276 277 // See if there is already a GEP with these indices. If not, check to 278 // make sure that we aren't promoting too many elements. If so, nothing 279 // to do. 280 if (std::find(GEPIndices.begin(), GEPIndices.end(), Operands) == 281 GEPIndices.end()) { 282 if (GEPIndices.size() == 3) { 283 DOUT << "argpromotion disable promoting argument '" 284 << Arg->getName() << "' because it would require adding more " 285 << "than 3 arguments to the function.\n"; 286 // We limit aggregate promotion to only promoting up to three elements 287 // of the aggregate. 288 return false; 289 } 290 GEPIndices.push_back(Operands); 291 } 292 } else { 293 return false; // Not a load or a GEP. 294 } 295 296 if (Loads.empty()) return true; // No users, this is a dead argument. 297 298 // If we decide that we want to promote this argument, the value is going to 299 // be unconditionally loaded in all callees. This is only safe to do if the 300 // pointer was going to be unconditionally loaded anyway (i.e. there is a load 301 // of the pointer in the entry block of the function) or if we can prove that 302 // all pointers passed in are always to legal locations (for example, no null 303 // pointers are passed in, no pointers to free'd memory, etc). 304 if (!SafeToUnconditionallyLoad && 305 !AllCalleesPassInValidPointerForArgument(Arg)) 306 return false; // Cannot prove that this is safe!! 307 308 // Okay, now we know that the argument is only used by load instructions and 309 // it is safe to unconditionally load the pointer. Use alias analysis to 310 // check to see if the pointer is guaranteed to not be modified from entry of 311 // the function to each of the load instructions. 312 313 // Because there could be several/many load instructions, remember which 314 // blocks we know to be transparent to the load. 315 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 316 317 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 318 TargetData &TD = getAnalysis<TargetData>(); 319 320 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 321 // Check to see if the load is invalidated from the start of the block to 322 // the load itself. 323 LoadInst *Load = Loads[i]; 324 BasicBlock *BB = Load->getParent(); 325 326 const PointerType *LoadTy = 327 cast<PointerType>(Load->getOperand(0)->getType()); 328 unsigned LoadSize = (unsigned)TD.getTypeStoreSize(LoadTy->getElementType()); 329 330 if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) 331 return false; // Pointer is invalidated! 332 333 // Now check every path from the entry block to the load for transparency. 334 // To do this, we perform a depth first search on the inverse CFG from the 335 // loading block. 336 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 337 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 338 I = idf_ext_begin(*PI, TranspBlocks), 339 E = idf_ext_end(*PI, TranspBlocks); I != E; ++I) 340 if (AA.canBasicBlockModify(**I, Arg, LoadSize)) 341 return false; 342 } 343 344 // If the path from the entry of the function to each load is free of 345 // instructions that potentially invalidate the load, we can make the 346 // transformation! 347 return true; 348} 349 350namespace { 351 /// GEPIdxComparator - Provide a strong ordering for GEP indices. All Value* 352 /// elements are instances of ConstantInt. 353 /// 354 struct GEPIdxComparator { 355 bool operator()(const std::vector<Value*> &LHS, 356 const std::vector<Value*> &RHS) const { 357 unsigned idx = 0; 358 for (; idx < LHS.size() && idx < RHS.size(); ++idx) { 359 if (LHS[idx] != RHS[idx]) { 360 return cast<ConstantInt>(LHS[idx])->getZExtValue() < 361 cast<ConstantInt>(RHS[idx])->getZExtValue(); 362 } 363 } 364 365 // Return less than if we ran out of stuff in LHS and we didn't run out of 366 // stuff in RHS. 367 return idx == LHS.size() && idx != RHS.size(); 368 } 369 }; 370} 371 372 373/// DoPromotion - This method actually performs the promotion of the specified 374/// arguments, and returns the new function. At this point, we know that it's 375/// safe to do so. 376Function *ArgPromotion::DoPromotion(Function *F, 377 SmallPtrSet<Argument*, 8> &ArgsToPromote, 378 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 379 380 // Start by computing a new prototype for the function, which is the same as 381 // the old function, but has modified arguments. 382 const FunctionType *FTy = F->getFunctionType(); 383 std::vector<const Type*> Params; 384 385 typedef std::set<std::vector<Value*>, GEPIdxComparator> ScalarizeTable; 386 387 // ScalarizedElements - If we are promoting a pointer that has elements 388 // accessed out of it, keep track of which elements are accessed so that we 389 // can add one argument for each. 390 // 391 // Arguments that are directly loaded will have a zero element value here, to 392 // handle cases where there are both a direct load and GEP accesses. 393 // 394 std::map<Argument*, ScalarizeTable> ScalarizedElements; 395 396 // OriginalLoads - Keep track of a representative load instruction from the 397 // original function so that we can tell the alias analysis implementation 398 // what the new GEP/Load instructions we are inserting look like. 399 std::map<std::vector<Value*>, LoadInst*> OriginalLoads; 400 401 // ParamAttrs - Keep track of the parameter attributes for the arguments 402 // that we are *not* promoting. For the ones that we do promote, the parameter 403 // attributes are lost 404 ParamAttrsVector ParamAttrsVec; 405 const ParamAttrsList *PAL = F->getParamAttrs(); 406 407 unsigned index = 1; 408 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 409 ++I, ++index) { 410 if (ByValArgsToTransform.count(I)) { 411 // Just add all the struct element types. 412 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 413 const StructType *STy = cast<StructType>(AgTy); 414 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 415 Params.push_back(STy->getElementType(i)); 416 ++NumByValArgsPromoted; 417 } else if (!ArgsToPromote.count(I)) { 418 Params.push_back(I->getType()); 419 if (unsigned attrs = PAL ? PAL->getParamAttrs(index) : 0) 420 ParamAttrsVec.push_back(ParamAttrsWithIndex::get(Params.size(), attrs)); 421 } else if (I->use_empty()) { 422 ++NumArgumentsDead; 423 } else { 424 // Okay, this is being promoted. Check to see if there are any GEP uses 425 // of the argument. 426 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 427 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 428 ++UI) { 429 Instruction *User = cast<Instruction>(*UI); 430 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 431 std::vector<Value*> Indices(User->op_begin()+1, User->op_end()); 432 ArgIndices.insert(Indices); 433 LoadInst *OrigLoad; 434 if (LoadInst *L = dyn_cast<LoadInst>(User)) 435 OrigLoad = L; 436 else 437 OrigLoad = cast<LoadInst>(User->use_back()); 438 OriginalLoads[Indices] = OrigLoad; 439 } 440 441 // Add a parameter to the function for each element passed in. 442 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 443 E = ArgIndices.end(); SI != E; ++SI) 444 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), 445 SI->begin(), 446 SI->end())); 447 448 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 449 ++NumArgumentsPromoted; 450 else 451 ++NumAggregatesPromoted; 452 } 453 } 454 455 const Type *RetTy = FTy->getReturnType(); 456 457 // Recompute the parameter attributes list based on the new arguments for 458 // the function. 459 PAL = ParamAttrsList::get(ParamAttrsVec); 460 461 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 462 // have zero fixed arguments. 463 bool ExtraArgHack = false; 464 if (Params.empty() && FTy->isVarArg()) { 465 ExtraArgHack = true; 466 Params.push_back(Type::Int32Ty); 467 } 468 469 // Construct the new function type using the new arguments. 470 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 471 472 // Create the new function body and insert it into the module... 473 Function *NF = new Function(NFTy, F->getLinkage(), F->getName()); 474 NF->setCallingConv(F->getCallingConv()); 475 NF->setParamAttrs(PAL); 476 if (F->hasCollector()) 477 NF->setCollector(F->getCollector()); 478 F->getParent()->getFunctionList().insert(F, NF); 479 480 // Get the alias analysis information that we need to update to reflect our 481 // changes. 482 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 483 484 // Loop over all of the callers of the function, transforming the call sites 485 // to pass in the loaded pointers. 486 // 487 std::vector<Value*> Args; 488 while (!F->use_empty()) { 489 CallSite CS = CallSite::get(F->use_back()); 490 Instruction *Call = CS.getInstruction(); 491 492 // Loop over the operands, inserting GEP and loads in the caller as 493 // appropriate. 494 CallSite::arg_iterator AI = CS.arg_begin(); 495 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 496 I != E; ++I, ++AI) 497 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 498 Args.push_back(*AI); // Unmodified argument 499 } else if (ByValArgsToTransform.count(I)) { 500 // Emit a GEP and load for each element of the struct. 501 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 502 const StructType *STy = cast<StructType>(AgTy); 503 Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 }; 504 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 505 Idxs[1] = ConstantInt::get(Type::Int32Ty, i); 506 Value *Idx = new GetElementPtrInst(*AI, Idxs, Idxs+2, 507 (*AI)->getName()+"."+utostr(i), 508 Call); 509 // TODO: Tell AA about the new values? 510 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 511 } 512 } else if (!I->use_empty()) { 513 // Non-dead argument: insert GEPs and loads as appropriate. 514 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 515 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 516 E = ArgIndices.end(); SI != E; ++SI) { 517 Value *V = *AI; 518 LoadInst *OrigLoad = OriginalLoads[*SI]; 519 if (!SI->empty()) { 520 V = new GetElementPtrInst(V, SI->begin(), SI->end(), 521 V->getName()+".idx", Call); 522 AA.copyValue(OrigLoad->getOperand(0), V); 523 } 524 Args.push_back(new LoadInst(V, V->getName()+".val", Call)); 525 AA.copyValue(OrigLoad, Args.back()); 526 } 527 } 528 529 if (ExtraArgHack) 530 Args.push_back(Constant::getNullValue(Type::Int32Ty)); 531 532 // Push any varargs arguments on the list 533 for (; AI != CS.arg_end(); ++AI) 534 Args.push_back(*AI); 535 536 Instruction *New; 537 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 538 New = new InvokeInst(NF, II->getNormalDest(), II->getUnwindDest(), 539 Args.begin(), Args.end(), "", Call); 540 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 541 cast<InvokeInst>(New)->setParamAttrs(PAL); 542 } else { 543 New = new CallInst(NF, Args.begin(), Args.end(), "", Call); 544 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 545 cast<CallInst>(New)->setParamAttrs(PAL); 546 if (cast<CallInst>(Call)->isTailCall()) 547 cast<CallInst>(New)->setTailCall(); 548 } 549 Args.clear(); 550 551 // Update the alias analysis implementation to know that we are replacing 552 // the old call with a new one. 553 AA.replaceWithNewValue(Call, New); 554 555 if (!Call->use_empty()) { 556 Call->replaceAllUsesWith(New); 557 New->takeName(Call); 558 } 559 560 // Finally, remove the old call from the program, reducing the use-count of 561 // F. 562 Call->eraseFromParent(); 563 } 564 565 // Since we have now created the new function, splice the body of the old 566 // function right into the new function, leaving the old rotting hulk of the 567 // function empty. 568 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 569 570 // Loop over the argument list, transfering uses of the old arguments over to 571 // the new arguments, also transfering over the names as well. 572 // 573 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 574 I2 = NF->arg_begin(); I != E; ++I) { 575 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 576 // If this is an unmodified argument, move the name and users over to the 577 // new version. 578 I->replaceAllUsesWith(I2); 579 I2->takeName(I); 580 AA.replaceWithNewValue(I, I2); 581 ++I2; 582 continue; 583 } 584 585 if (ByValArgsToTransform.count(I)) { 586 // In the callee, we create an alloca, and store each of the new incoming 587 // arguments into the alloca. 588 Instruction *InsertPt = NF->begin()->begin(); 589 590 // Just add all the struct element types. 591 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 592 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 593 const StructType *STy = cast<StructType>(AgTy); 594 Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 }; 595 596 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 597 Idxs[1] = ConstantInt::get(Type::Int32Ty, i); 598 Value *Idx = new GetElementPtrInst(TheAlloca, Idxs, Idxs+2, 599 TheAlloca->getName()+"."+utostr(i), 600 InsertPt); 601 I2->setName(I->getName()+"."+utostr(i)); 602 new StoreInst(I2++, Idx, InsertPt); 603 } 604 605 // Anything that used the arg should now use the alloca. 606 I->replaceAllUsesWith(TheAlloca); 607 TheAlloca->takeName(I); 608 AA.replaceWithNewValue(I, TheAlloca); 609 continue; 610 } 611 612 if (I->use_empty()) { 613 AA.deleteValue(I); 614 continue; 615 } 616 617 // Otherwise, if we promoted this argument, then all users are load 618 // instructions, and all loads should be using the new argument that we 619 // added. 620 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 621 622 while (!I->use_empty()) { 623 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 624 assert(ArgIndices.begin()->empty() && 625 "Load element should sort to front!"); 626 I2->setName(I->getName()+".val"); 627 LI->replaceAllUsesWith(I2); 628 AA.replaceWithNewValue(LI, I2); 629 LI->eraseFromParent(); 630 DOUT << "*** Promoted load of argument '" << I->getName() 631 << "' in function '" << F->getName() << "'\n"; 632 } else { 633 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 634 std::vector<Value*> Operands(GEP->op_begin()+1, GEP->op_end()); 635 636 Function::arg_iterator TheArg = I2; 637 for (ScalarizeTable::iterator It = ArgIndices.begin(); 638 *It != Operands; ++It, ++TheArg) { 639 assert(It != ArgIndices.end() && "GEP not handled??"); 640 } 641 642 std::string NewName = I->getName(); 643 for (unsigned i = 0, e = Operands.size(); i != e; ++i) 644 if (ConstantInt *CI = dyn_cast<ConstantInt>(Operands[i])) 645 NewName += "." + CI->getValue().toStringUnsigned(10); 646 else 647 NewName += ".x"; 648 TheArg->setName(NewName+".val"); 649 650 DOUT << "*** Promoted agg argument '" << TheArg->getName() 651 << "' of function '" << F->getName() << "'\n"; 652 653 // All of the uses must be load instructions. Replace them all with 654 // the argument specified by ArgNo. 655 while (!GEP->use_empty()) { 656 LoadInst *L = cast<LoadInst>(GEP->use_back()); 657 L->replaceAllUsesWith(TheArg); 658 AA.replaceWithNewValue(L, TheArg); 659 L->eraseFromParent(); 660 } 661 AA.deleteValue(GEP); 662 GEP->eraseFromParent(); 663 } 664 } 665 666 // Increment I2 past all of the arguments added for this promoted pointer. 667 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 668 ++I2; 669 } 670 671 // Notify the alias analysis implementation that we inserted a new argument. 672 if (ExtraArgHack) 673 AA.copyValue(Constant::getNullValue(Type::Int32Ty), NF->arg_begin()); 674 675 676 // Tell the alias analysis that the old function is about to disappear. 677 AA.replaceWithNewValue(F, NF); 678 679 // Now that the old function is dead, delete it. 680 F->eraseFromParent(); 681 return NF; 682} 683